This application relates to a scroll compressor wherein one set of ports is utilized for both injecting vapor refrigerant into the compressor and for compressor unloading by directing vapor refrigerant from the compressor intermediate compression point to compressor suction, and wherein the other separate set of ports is utilized only for compressor unloading.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, first and second scroll members each have a base and a generally spiral wrap extending from the base. The wraps of the two scroll members interfit to define compression chambers. One of the two scroll members is caused to orbit relative to the other, and as they orbit relative to each other, refrigerant is trapped within compression chambers defined between the wraps. As the orbiting scroll moves through an orbiting cycle, the size of these compression chambers is reduced and the entrapped refrigerant is compressed.
There are many optional features which are utilized in refrigerant compression applications, and in scroll compressors. In one optional feature, when there is a reduced cooling capacity desired from a refrigerant system associated with the scroll compressor, the compressor may be “unloaded”. When the compressor is unloaded, refrigerant may be tapped from the compression chambers through an open unloader valve and back to a suction port leading into the compressor. In this manner, the amount of compressed refrigerant is reduced, and the capacity of the associated refrigerant system is similarly reduced.
In another optional feature, when additional capacity is desired, an economizer cycle may be actuated. With an economizer cycle, refrigerant downstream of a condenser is tapped from a main refrigerant flow line and the tapped refrigerant is expanded. The tapped refrigerant passes in a heat transfer relationship with the main refrigerant line in an economizer heat exchanger, thereby sub-cooling the main refrigerant flow. The tapped refrigerant is injected into an intermediate compression port or set of ports in the compressor.
There is a prior art construction which provides both the unloader and economizer functions through to the same flow passage in the non-orbiting scroll member. In this structure, the economizer injection passage is also connected to the unloader line which selectively communicates the economizer injection passage back to the suction line. The economizer injection passage can be kept open or shutoff, with the shut off device installed in the economizer line between the condenser and the unloader line. Separate flow control devices control the operation of both the economizer function and the unloader. To perform vapor injection economized function or by-pass of the flow back to suction, there is normally a passage that extends through the base of the non-orbiting scroll, and into ports leading into the compression chambers.
In the prior art, there have been compromises with regard to the size and position of these ports. For optimum economizer operation (vapor injection), it is desirable to have relatively small ports. If the ports for injection are selected to be too large, the efficiency of the compression cycle would drop off. On the other hand, for optimum unloader operation, it is normally desirable to select the ports to be as large as possible as permitted by the compressor dimensional envelope.
Thus, in the prior art, there have been compromises between these two goals, when selecting the size of these ports, since the same ports were used for both vapor injection and by-pass unloading operation.